One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disk drive. The most basic parts of a disk drive are a disk that is rotated, an actuator that moves a transducer to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. The disk drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disk surface. A microprocessor controls most of the operations of the disk drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disk.
The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disk in a transducing relationship with the disk. The transducer can be used to read information representing data from the disk or write information representing data to the disk. When the disk is operating, the disk is usually spinning at relatively high RPM. These days common rotational speeds are 5100 and 7200 RPM. Rotational speeds of 10,000 RPM and higher are contemplated for the future. At such speeds, the very small ceramic block flies on a very thin layer of gas or air. In operation, the distance between the small ceramic block and the disk is very small. Currently "fly" heights are about 0.0003 mm. In some disk drives, the ceramic block does not fly on a cushion of air but rather passes through a layer of lubricant on the disk.
Information representative of data is stored on the surface of the memory disk. Disk drive systems read and write information stored on tracks on memory disks. Transducers, in the form of read/write heads, located on both sides of the memory disk, read and write information on the memory disks when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disk. The transducer is also said to be moved to a target track. As the memory disk spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disk. Similarly, reading data on a memory disk is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disk. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disk drives, the tracks are a multiplicity of concentric circular tracks. In other disk drives, a continuous spiral is one track on one side of a disk drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The actuator assembly is composed of many parts that contribute to the performance required to accurately hold the read/write head in the proper position. An actuator includes a pivot assembly, an arm, a voice coil yoke assembly and a head gimbal suspension assembly. A suspension or load beam is part of the head gimbal suspension assembly.
One end of the suspension is attached to the actuator arm. The read/write head is found attached to the other end of the suspension. One end of the actuator arm is coupled to a pivot assembly. The pivot assembly is in turn connected to a servo motor system through the voice coil yoke. The other end is attached to the head gimbal suspension assembly. The head gimbal suspension assembly allows the read/write head to gimbal for pitch and roll to follow the topography of the imperfect memory disk surface. The head gimbal assembly also restricts motion with respect to the radial and circumferential directions of the memory disk. The suspension is coupled to the actuator arm as part of the mounting support holding the pivot support and coupled to the servo motor. Currently, the pivot assembly is mounted within an opening in a unitized E-block. The E-block includes arms for mounting the suspension on one end and a voice coil yoke on the other end. U.S. Pat. No. 5,283,704 issued to Reidenbach illustrates another actuator system composed of individual components instead of the unitized E-block. This actuator system is "built up" from an actuator arm, spacer rings, a separate voice coil yoke frame assembly, and a separate bearing cartridge. A voice coil is located on the voice coil yoke. The voice coil and magnets attached to the housing of the disk drive form a voice coil motor. The disk drive includes a feedback control loop to enable accurate positioning of the transducer. The disk drive system sends control signals to the voice coil motor to move the actuator arm and the suspension supporting the read/write head across the memory disk in a radial direction to the target track. The control signals indicate to the motor the magnitude and direction of the displacement. The control signals can also be used to maintain the position of the read/write head or transducer over a particular track.
To minimize noise and the inductance of the leads, the preamplifier and write-current sources are usually placed near the actuator arms. Wires or leads are typically strung over the surface of the actuator arm and pass to the preamplifier attached near the actuator arm. The wires are typically twisted in pairs to minimize cross talk between the wires. Cross talk results in noise in the wires which may produce inaccurate readback signals sent to the preamplifier. Minimizing noise from the preamplifier is critical since noise from the preamplifier may produce dominating noise in the amplifiers which follow in the channel circuitry. Moving the preamplifier as close to the transducer as possible minimizes noise in the leads and noise produced in the channel circuit. In addition, moving the chip closer to the transducer improves the frequency response of the head and the preamplifier chip as a function of the interconnect impedance.
In the past, various industry pundits determined that it would be very advantageous to place a preamplifier or channel chip on the actuator arm in a rotary actuator disk drive. Chips have been placed on the arms of some linear actuators where interdisk spacing, and the weight of the arm were not concerns. Placing the chip on the thin stainless steel arms or suspension load beams associated with today's disk drives with rotary actuators could not be done since the heat produced cannot be dissipated by a thin, stainless steel actuator arm or suspension. A chip could be placed on thick aluminum arms or E blocks, but the benefit would be minimal since the head and transducer would still be 25 mm or more away. Some current disk drive designs have the chip mounted in the flex cable attaching to the base of the arm, so moving the chip to the end of the arm using conventional arm and suspension lengths would produce minimal benefit.
There were also problems with spacing between the arms of a disk drive. When a preamplifier chip in conventional packaging and flex circuits was added to the arm, the spacing between the disks would have to be increased to accommodate the thickness of the chip package. Pockets could not be formed in the stainless steel arm since the material is too thin to dissipate the heat generated by the chips.
There is always a need for channels with less noise. Channels with less noise have lower read error rates. In addition, if the signal is easier to read, the data retrieval process may be able to be conducted more quickly with lesser need for error correction codes and error correction procedures. Consequently, there is always a need for a more noise free signal to increase the reliability of the channel and increase the integrity of the data stored on the disk.